Protactinium(IV) oxide is a chemical compound with the formula PaO2. The black oxide is formed by reducing Pa2O5 with hydrogen at 1 550 °C. Protactinium(IV) oxide does not dissolve in H2SO4, HNO3, or HCl solutions, but reacts with the HF.[1][2]:195

As protactinium(IV) oxide, like other protactinium compounds, is radioactive, toxic and very rare, it has no known technological use.